Michael A. E. Ramsay M.D.
Introduction
Virtually every patient admitted into the intensive care unit (ICU) is
administered sedation therapy. The precise control of the depth of
sedation is often not well managed. Patients are frequently over or
under-sedated with, as a result of this lack of control, an accompanying
increase in morbidity, mortality and economic cost.
Over 25 years ago, an attempt was initiated to bring the control of
sedation level up to the same level of intense management as the control
of hemodynamics, fluid and electrolyte balances, oxygen and metabolic
parameters [1]. This concept has taken a long time to reach the critical
care pathway of the majority of ICUs. However, economic issues and
advances in pharmacology, have lead to a critical re-evaluation of
sedation techniques, so that the goal of a heavily sedated or comatose
patient for the maintenance of ventilator synchrony, is now changing to
the goal, where possible, of a calm, co-operative, comfortable and
communicative patient, who can interact with family members and medical
staff. This change in practice pattern has resulted in shorter periods of
time on mechanical ventilation support, leading to a shorter stay in the
intensive care unit [2,3].
Sedation goals
The effective management of pain, anxiety and sleep (hypnosis) are the
major aims of a sedation therapy regimen. The ICU environment frequently
lends itself to being an unpleasant experience for the critically ill
patient. The patient is exposed to numerous ominous and frightening
procedures that are a necessary part of the care process. In an effort to
make this clinical arena a more humane place to be treated, sedation
therapy is administered. The careful and precise control of sedation
therapy may lead to better control of the patient requiring mechanical
ventilation support, and reduce the requirement for the use of
neuromuscular blocking agents.
The desired result of a sedation regimen is to allow the patient to
tolerate the physical environment, and the unpleasant procedures and
therapies that are necessary in the ICU; to facilitate nursing care and
management, and reduce both anxiety and stress, so that post-traumatic
stress disorder does not occur after discharge from the unit. Patient
safety is paramount, and the avoidance of self-extubation and inadvertent
removal of catheters and other life dependency equipment is essential.
Amnesia is probably another useful goal of sedation therapy, so that the
patient has no recall of unpleasant events or surroundings. It has,
however, been suggested that patients recovering from intensive care
therapy, may have an unrealistic outlook on their recovery, if they have
no recall on the severity of their illness [4].
The blunting of autonomic responses, reduced oxygen consumption and
ventilator synchrony are other important goals of sedation therapy. The
maintenance of a normal sleep pattern can help maintain psychological
well-being, as well as preventing exhaustion and the loss of a desire to
survive. Patient agitation is another common problem in the critical care
unit, it may result from a specific cause such as hypoxia, under
ventilation, metabolic derangement and other correctable entities that
should be addressed first, but it may be the result of sleep deprivation,
or pharmacological interactions, and require sedation to control [5-9]
Pain management
The effective management of pain is essential in the proper management of
sedation, and results in improved patient satisfaction, a faster recovery
with reduced complications [10]. This has to be the priority when
assessing a patient's sedation requirements. Adequate analgesia may reduce
the necessity for other sedative therapy. Nearly all patients in the ICU
experience pain, whether it is the result of procedures performed on them,
the disease process, catheters or tubes inserted into them, or because
they are immobile and cannot shift position. If the patient is paralyzed
or obtunded, they will have lost the ability to communicate the severe
discomfort that they may be in, to the care team. The sequelae of severe
untreated pain can be long lasting psychological effects on the patient,
together with adverse haemodynamic changes. Tachycardia and hypertension,
together with an increase in systemic vascular resistance, will cause an
increase in myocardial oxygen consumption and demand, that may result in
myocardial ischemia [10]. There may also be a deleterious effect on the
immune system in an all ready compromized patient who is trying to combat
a serious illness, but foremost it is inhumane not to adequately treat
pain. The precise control of pain can reduce the need for deep sedation
and reduce the necessity for muscle relaxants. The mainstay of analgesic
therapy is still the opiates. Morphine or fentanyl are two of the
narcotics most frequently administered in the ICU. They are effective pain
relievers, but come with significant side effects, that may have a
deleterious effect on the patient [11]. The balance between the adverse
effects of the opioid analgesics, and the beneficial effect of analgesia,
is a limiting factor in their use and the appropriate pain therapy
delivered to these critically ill patients. These adverse effects include
respiratory depression, deep sedation, narcotic bowel syndrome, pruritus,
nausea, vomiting and a decreased ability to communicate. Nearly all the
narcotics have active metabolites that will cause a prolongation of their
effects when continually administered to patients with multi-organ system
failure. This is the common profile for the intensive care patient;
therefore there may be an insidious build up in the narcotic actions of
these agents. Remifentanil, a relatively new, mu-receptor specific opiate
that is rapidly metabolized by non-specific esterases into metabolites
with very weak narcotic activity, may have a future role to play in the
close control of pain in the critically ill patient [12].
Over sedation
The results of over sedation in the mechanically ventilated patient are an
increased time being ventilated, an increased time in the intensive care
unit, and an increased cost of care. The common effect of an increasing
dose of most sedative agents is respiratory depression. This may
facilitate ventilator synchrony, but will prolong the weaning process. In
the extubated patient it may be associated with severe hypercarbia,
hypoxia and respiratory arrest.
There is no sensitive monitor of respiratory depression in the extubated
patient, who is receiving supplementary oxygen. Under these circumstances,
the only parameters that correlate well with respiratory depression are
respiratory pattern and level of consciousness. Respiratory rate and
end-tidal carbon dioxide measured via a nasal cannula, are not reliable
monitors of depressed respiration [13]. The pulse oximeter is a LATE detector
of respiratory depression, when there is an increased concentration of
inspired oxygen [14].
Under sedation
The untoward effects of under sedation include an increased production of
endogenous catecholamines, that results in an increase in blood pressure,
heart rate and myocardial oxygen consumption. The patient may be at risk
for self injury from the accidental removal of the endotracheal tube or
vital catheters. The mental sequelae from being awake while painful, and
terrifying procedures are performed on the patient can be the development
of a post-traumatic stress disorder, that may require prolonged therapy
after discharge [15]. The patients’ who are unresponsive because of the
administration of neuromuscular blocking drugs are most at risk [16].
Sleep deprivation is very common, and can result in the development of the
typical ICU psychosis [17].
Controlled Sedation
To prevent the adverse complications of poorly controlled sedation,
sedation therapy should be administered in a careful and precise manner.
The depth of sedation should be clearly defined and the infusion of
sedative drug precisely targeted to this clinical endpoint. If the patient
is sedated to an unrousable depth, then unless clinically contraindicated,
they should be brought to a level where a neurological assessment can be
made every 24 hours [18]. In his manner a cerebral insult will not go
undetected. By defining the sedation level and carefully controlling the
sedation infusion to meet this endpoint, the dangers of over or under
sedation are minimized. It will also provide for continuity of care, as
all care-givers understand the required depth of sedation.
To be able to reach this goal the routine use of sedation scales is
essential. The scoring system selected for use must be easily understood,
used routinely and be part of the regular assessment of the ICU patient In
fact sedation scoring systems should be in regular use where ever potent
respiratory depressant drugs are being used.
Sedation Scoring Systems.
A sedation scoring system should be an integral component of any sedation
protocol. The four most validated scoring systems include: The Ramsay
Sedation Scale; The Sedation Agitation Scale; The Motor Activity
Assessment Scale and for the pediatric population: The Comfort Scale [19].
Ramsay Sedation Scale
The Ramsay Sedation Scale (RSS, Table), was the first scale to be defined
and was designed as a test of rousability. The RSS scores sedation at six
different levels, according to how rousable the patient is. It is an
intuitively obvious scale and therefore lends itself to universal use, not
only in the ICU, but wherever sedative drugs or narcotics are given. It
can be added to the pain score and be considered the sixth vital sign.
1 Patient is anxious and agitated or restless, or both
2 Patient is co-operative, oriented, and tranquil
3 Patient responds to commands only
4 Patient exhibits brisk response to light glabellar tap or loud auditory
stimulus
5 Patient exhibits a sluggish response to light glabellar tap or loud
auditory stimulus
6 Patient exhibits no response
The RSS defines the conscious state from a level 1: the patient is
anxious, agitated or restless, through the continuum of sedation to a
level 6: the patient is completely unresponsive. Therefore when an
assessment is to be made, the first decision to be made is to note if the
patient is awake. If the patient is awake: are they anxious, agitated or
restless (RSS 1) or are they calm, co-operative and communicative (RSS 2)?
If the patient is asleep then a test of reusability needs to be made. If
the patient responds quickly to a voice command, this is a RSS 3. If the
response is slow then the patient is assigned a level 4. If the patient
does not respond a stronger stimulus is applied. A louder auditory
stimulus or a glabellar (between the eyebrows) tap is enacted. A brisk
response to this test of rousabilty places the patient at a RSS 4. A slow
or sluggish response categorizes the patient to a RSS 5. No response at
all places the patient at a level 6.
The rousability stimulus was specifically designed not to be a painful
test and not to startle the patient. In fact it was planned that a
sleeping patient would not be roused to a fully awakened state, so that
the sleep pattern would not be disturbed.
A disadvantage of the RSS is that it relies on the ability of the patient
to respond, therefore the patient who has received neuromuscular blocking
drugs cannot be assessed in this manner. Also at a level 1 score, there is
no further definition of the degree of agitation, and there are occasions
when this may be important to record. The Sedation-Agitation Scale does
take this into consideration [20]. At the deep end of the scale, a RSS 6,
there is no further information as to whether the patient is in a light
plane of general anesthesia or deep coma. This assessment can be made from
monitoring the compressed spectral array signal from an
electroencephalogram, A bispectral index score of 61.7 correlates well
with a RSS of 6 [21].
Conclusion
Despite the ready availability of sedation scales over the last 25 years,
a review of ICU practice reveals that many units still do not closely
control the level of sedation in their critically ill patients. In those
units where sedation scoring systems are used fewer than half the patients
are at the prescribed level for more than 50% of the time. Therefore there
is still an opportunity to educate the importance of the dynamics of
assessment, re-assessment and adjustment in the rate of delivery of
sedative. This dynamic is essential to avoid the complications associated
with over and under sedation.
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